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7.04 Biological Drawings

Posted10/11/2024
Updated23/12/2024
ByBMF
Views91

Microscopy Drawing Guide

1. Introduction

Microscopy drawings are essential for accurately representing biological specimens observed under a microscope. They are divided into two main types: Low Power Drawings and High Power Drawings. Understanding the distinct purposes and guidelines for each type ensures clear and effective scientific illustrations.

2. Types of Microscopy Drawings

A. Low Power Drawings

Guidelines:

  • Identify the Tissue:
    • For low power drawings, you just want to have an overall outline of the different tissues.
    • If it helps, use high power magnification to identify different tissues.
    • Completely enclose each tissue with clear boundary lines.
  • Simplify Representation:
    • Do Not draw individual cells; focus on tissue distribution.
    • Avoid filling spaces with cells to prevent gaps between tissues.
  • Accuracy:
    • Represent tissue distribution based on observation, not textbook images or what you think it should look like.
  • Use Representative Portions:
    • For symmetrical structures, draw a representative section (e.g., half of a transverse section of root or stem).
    • For leaves, include half a midrib and a small portion of the adjacent lamina.
  • Scale Appropriately:
    • Ensure the drawing occupies at least half of the designated page space.
    • Enlarge all parts of drawing equally (keep the same uniform ratio and shape of the cells/tissue, just drawn larger).

  • Drawing Area:
    • Utilize the allocated space efficiently, covering around half to two-thirds of the provided area (rather draw large than too small).
    • Avoid drawing over text or page margins.

B. High Power Drawings

Guidelines:

  • Select Representative Cells:
    • Draw only a few adjacent cells (typically 2-3) to demonstrate cell structure and arrangement.
    • If cells are similar, three cells are often sufficient.
    • If they ask you to draw cells that are touching each other, make sure all 3 cells touch each of the other cells.
  • Simplify Cellular Components:
    • Do Not shade nuclei or nucleoli; draw only their outlines.
  • Drawing Size:
    • Ensure the drawing covers around two-thirds of the allocated space for clarity.
  • Avoid:
    • Inaccurate representation of cells.

3. Essential Tools

  • Sharp HB or H Pencil: For clear, precise pencil lines.
  • Eraser: To correct mistakes without damaging the paper.
  • Ruler: For drawing straight lines, measuring scales, and underlining headings.
  • Plain Paper: Use high-quality, unlined paper for clarity.
  • Pen: For labelling and headings only (do not use for the main drawing).

4. General Drawing Quality Standards

  • Line Usage:
    • Use clear, continuous pencil lines for the main drawing.
    • Do Not use a pen for the main drawing.
  • No Shading:
    • Avoid shading; only draw the outlines of objects, regardless of their actual darkness.
  • Proportions:
    • Ensure accurate proportions based on direct observation, not textbook images.
  • Scale Appropriately:
    • Draw the specimen to occupy at least half of the drawing page.
  • Drawing Area:
    • Make the drawing large enough to cover approximately two-thirds of the designated space.
    • Draw within the provided space, avoiding overlapping text or page margins.
  • Accuracy and Clarity:
    • Draw what you see under the microscope, not what you expect based on prior knowledge.
    • Maintain precise and neat lines using a sharp pencil and ruler.

5. Labelling Standards

  • Writing Tools:
    • Use pen for all labels and headings.
    • Use pencil for label lines to allow corrections and maintain clarity.
  • Headings:
    • Each drawing should have a heading written in pen.
    • Underline the heading using a ruler and pen for neatness.
  • Label Placement:
    • Labels should be horizontal and aligned neatly, typically on the right side of the drawing.
    • Arrange labels below each other to avoid clutter.
  • Label Lines:
    • Use straight lines drawn with a ruler.
    • Do Not use arrowheads; label lines should be straight without any arrowheads.
  • Annotations:
    • Add explanatory notes if necessary to clarify specific features.

6. Magnification and Scale

A. Calculating Magnification

  • Formula:
  • Example Calculation:
    • If magnification is 400× and a scale line in the drawing is 40 mm: 40 mm (drawing) = 400 μm (specimen)
    • Steps:
      1. Write the formula for magnification.
      2. Substitute the given values with appropriate units.

B. Scale Line

  • Purpose: Represents the real size of structures within the specimen.
  • Placement: Typically placed at the bottom of the drawing.
  • Example:
    • At 400× magnification, a 40 mm scale line in the drawing corresponds to 400 μm in the specimen.

7. Common Errors in Drawings

  • Arrowheads on Label Lines: Label lines should be straight without any arrowheads.
  • Use of Shading: Shading is not allowed in scientific drawings; only outlines should be drawn.
  • Overlapping or Disconnected Lines: Ensure lines are clear and connected to avoid confusion.
  • Incorrect Proportions: Maintain accurate proportions based on observation to reflect true tissue distribution and cell structures.
  • Uneven or Crossed Label Lines: Labels should be neatly aligned without overlapping lines.
  • Drawing with a Pen: All main drawings should be done in pencil; pens are only for labels and headings.
  • Labelling Mistakes: Avoid using pens for label lines or writing labels in pencil.

8. Examples for Reference: High Power Drawings

A. Mouse Pancreas Section

  • Figures A:
    • Display photomicrographs alongside low and high power drawings.

Figure A: Photomicrograph of part of a section of the pancreas of a mouse taken at low power.

  • Examples (of drawings submitted by students):

Critique:

Good:

  • Both drawings have a heading.
  • Both indicate the magnification.

Bad:

  • The overall shape is different between the two examples. The drawing on the left is the more accurate shape.
  • The label lines are not horizontal.
  • The labels on the right specifically do not line up below each other.
  • The drawing on the right has some thicker and thinner lines (aka, shading).
  • In both drawings, it seems that the drawing and the writing is in pen or pencil.

B. Beech Leaf Sections (Fagus)

  • Figures B:
    • Show photomicrographs and corresponding low and high power drawings.
    • Compare leaves from sunny and shaded conditions.

Figure B: High power photomicrograph of the pancreas shown in Figure A

Examples (of drawings submitted by students):

Critique:

Good:

  • Both drawings have a heading.
  • Both indicate the magnification.

Bad:

  • In both drawings, it seems that the drawing and the writing is in pen or pencil.
  • The drawing on the left is definitely too small.
  • Both drawings seemed to have used shading and made the nuclei of the cells darker (all lines and structures should have the same thickness of pencil lines).
  • The spacing between the cells on the drawing on the left seems to be off. The drawing on the right seems to have the right amount/proportion of spacing.

C. Islet of Langerhans from the pancreas

Figure C: High power photomicrograph of an islet of Langerhans from the pancreas shown in Figure A

Examples (of drawings submitted by students):

Critique:

Good:

  • The general proportion of the cells seems to be ok.

Bad:

  • Read the comments on the side of the drawing for more information.

9. Examples for Reference: Low Power Drawings

D Transverse section of the lamina of a shade leaf of beech (Fagus)

Figure D: Photomicrograph of a transverse section of the lamina of a shade leaf of beech (Fagus) taken at low power.

Example (of drawings submitted by students):

The student has correctly drawn and labelled the different tissues, rather than drawn individual cells.

E Transverse section of the lamina of a sun leaf of beech

Figure E: Photomicrograph of a transverse section of the lamina of a sun leaf of beech taken at low power.
The student has correctly drawn and labelled the different tissues, rather than drawing individual cells.

F Transverse section of a dicot stem

Example (of drawings submitted by students):

The drawing made by the student on the right is far more accurate than the one on the left.

Other Examples:

11. Summary

  • Practice and Accuracy: Regular practice and a focus on accurate observation enhance drawing skills and the ability to effectively represent microscopic structures.
  • Low Power Drawings: Focus on accurately mapping the distribution and boundaries of tissues within an organ without depicting individual cells. Serve as a structural overview.
  • High Power Drawings: Highlight detailed cell structures and their arrangements, complementing low power drawings for a comprehensive understanding.
  • Essential Tools and Quality Standards: Utilize the correct tools and adhere to quality guidelines to ensure clear, accurate, and professional scientific drawings.
  • Labelling and Scale: Maintain precise and neat labeling standards, and accurately represent magnification and scale to reflect true specimen dimensions.
  • Avoid Common Errors: Be mindful of common pitfalls such as shading, incorrect proportions, and improper labeling to maintain the integrity of scientific drawings.

Practice Questions

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